A disk drive is a device implementing disk storage in which data is digitally recorded by various electronic magnetic optical or mechanical methods on disks (also referred to as the media). Disk storage is used in both computer storage and consumer electronic storage (e.g., audio CDs and video disks, standard DVD and Blu-Ray). To that end, disk drives may implement such disk storage with fixed or removable media. With removable media, the device is usually distinguished from the media as in a compact disk drive and a compact disk. Notable types of disk drives are the hard disk drive (HDD) containing a nonremovable disk, the floppy disk drive (FDD) and its removable floppy disk, and various optical disk drives and associated optical disk media.
A hard disk drive stores data onto tracks, heads, and sectors of a disk. A sector is a segment of a track, and the track is a circle of recorded data on a single recording surface or platter (an individual recording disk). The sector unit is the smallest size of data to be stored in a hard disk drive and each data file may have many sector units assigned to it. Digital disk drives are block storage devices. Each disk is divided into logical blocks (which may be larger or smaller than a physical sector). Blocks are addressed using their logical block addresses (LBA). Reading from or writing to a disk happens at the granularity of blocks.
The disk drive interface is the mechanism/protocol of communication between the rest of the system and the disk drive itself. Storage devices intended for desktop and mobile computers typically use ATA (Advanced Technology Attachment), PATA (Parallel ATA), and SATA (Serial ATA) interfaces. Enterprise systems and other storage devices typically use SCSI (Small Computer System Interface), SAS (serial-attached SCSI), and FC (Fibre Channel) interfaces in addition to some use of SATA.
Computer users are requiring an ever-increasing amount of disk drive storage space. Home computer users' increased storage of multimedia data, especially video and photographic data, has only served to increase the amount of storage space needed. Likewise, industry also requires increased storage space. As more and more business is being conducted electronically, there has been an ever-increasing demand and need for the storage of this vast amount of business data. Furthermore, there has been a demand to digitize the storage of once paper files in an attempt to decrease the overhead cost of this paper generation and storage.
Currently, the majority of this electronic data is stored on magnetic hard disk drive devices. However, the increased need of storage capacity has made current magnetic disk storage devices inadequate and a solution to this problem is necessary.
“Shingled Magnetic Recording,” (SMR) is a method of increasing the storage density of current magnetic hard disk drives. However, utilizing SMR devices requires a fundamentally new and different access model that allows random reads and only sequential writes.
A SMR device is divided into a configurable number of regions, called bands. The bands comprise tracks like standard magnetic recording devices and likewise these tracks comprise sectors. Unlike standard magnetic recording devices, the tracks on a SMR device are overlapped, also known as, shingled, thus increasing the storage density of the device. The bands of a SMR device may be configurable. This allows certain bands to be configured for “sequential access” while other bands on the same platter can be “random access” like traditional magnetic storage devices. A “sequential access band” supports random reads, but may only be written to sequentially. More precisely, data must be written starting at the beginning of the band, and may be added only in sequential order. Typically, any data already written in a sequential band cannot be changed, except by erasing the entire band and starting over at the beginning (for writing). A “random access band” supports random writes as well as reads, similar to existing hard disk drives, and does not possess the improved density of SMR sequential access bands.
SMR disk drives are being promoted as a means to increase the storage density of magnetic disk drives using current-generation technology. However, existing systems have no ability to cope with the different access model that SMR technology requires. Manufacturers plan to implement emulation strategies to make a SMR device behave like a traditional random-access device. However, some manufacturers have been amenable to providing a separate interface that exposes the native layout of the SMR device, along with its attendant limitations.
More information can be found here:
www.pdl.cmu.edu/ftp/News/newsletter11.pdf